1. Field of the Invention
The invention relates to a method for fabricating semiconductor device, and more particularly to a method for fabricating a vertical channel oxide semiconductor field-effect transistor (OSFET).
2. Description of the Prior Art
Attention has been focused on a technique for formation of a transistor using a semiconductor thin film formed over a substrate having an insulating surface. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) and an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor, and within which, oxide semiconductor containing indium (In), gallium (Ga), and zinc (Zn) has been attracting attention.
Conventional oxide semiconductor field effect transistors mostly have what is called a planar structure, in which elements such as oxide semiconductor layer and gate electrode are stacked over a plane. With advances in manufacturing process which enables miniaturization of such devices, various problems such as increase in short-channel effect and leakage current arise. Hence, how to effectively improve the drawbacks of current OSFETs have become an important task in this field.